Download Drill Problems

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PHYS 202 DRILL HOMEWORK PROBLEMS
PART 2
D2-1. The magnetic field lines of a bar magnet come out of the left side of the magnet and enter the right side.
Which side of the magnet should be labeled as the North pole? Which side should be labeled as the South
pole?
[left side is N, right side is S]
D2-2. Consider the loop of wire below. If a current flows clockwise, in which direction is the magnetic field
on the central axis of the loop? What if the current flows counterclockwise?
[clockwise makes field point into page;
counterclockwise makes field point out of page]
D2-3. Consider the straight segment of wire below. The current flowing through the wire creates a magnetic
field in the region around the wire. Find the directions of the field vectors at the points P, R, and S.
[P out of page; R into page; S into page]
P
R
S
I
D2-4. A straight wire segment is oriented so that the current is going into the page as shown. Find the
directions of the field vectors at the points P, R, and S.
[P up; R left; S right]
S
P
xI
R
D2-5. Current flows through the solenoid from P to Q. In which
direction does the magnetic field point on the long axis of the
solenoid? Which end of the solenoid is the North magnetic pole?
[Field points left. Left side is N pole.]
D2-6. A proton is traveling upwards. At its present position, the magnetic field is to the left. Find the
direction of the magnetic force on the proton.
[out of the page]
D2-7. An electron is traveling into the page. At its present position, the magnetic field is downwards. Find the
direction of the magnetic force on the electron.
[to the right]
D2-8. An electron is traveling at 2x106 m/s in the plane of the paper at an angle of 40 with respect to the
positive x-axis. At its present position, there is a magnetic field of 0.03 T directed along the positive yaxis. Find the size and direction of the magnetic force on the electron.
[7.35x10-15 N, into the page]
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D2-9. A 5 cm long straight wire segment carries 2 A of current and feels a magnetic force of 1.5x10-3 N
directed to the right. The wire is oriented vertically in the page with the current flowing upwards. Find the
size and direction of the magnetic field in the vicinity of the wire assuming that the filed direction is
perpendicular to the current direction.
[0.015 T, out of the page]
D2-10. A positive ion that had has one electron removed is initially traveling to the right at 3x106 m/s. It enters
a uniform magnetic field of 0.5 Teslas directed into the page. Does the ion travel in the clockwise or
counterclockwise in this field?
[counterclockwise]
D2-11. The ion in the previous problem travels along an arc with a radius of 25 cm. Find the mass of the ion.
[6.67x10-27 kg]
D2-12. A certain velocity selector uses a magnetic field of 250 Gauss. What size electric field must it use to
select a particle velocity of 5x106 m/s?
[125 kV/m]
D2-13. The velocity selector in the previous problem uses a magnetic field that is directed into the page and two
parallel plates oriented horizontally to supply the electric field. In which direction should the electric field
point if positively charged particles travel to the right through the selector? Which plate should be at the
higher voltage, the top or bottom plate?
[downward, top plate]
D2-14. Two ions with the same charge travel at the same speed into a region where the magnetic field is
perpendicular to their velocities. Both ions travel along circular arcs. Ion 1 is heavier than ion 2. Which
arc has the larger radius? Which ion feels a larger magnetic force?
[The arc of ion 1 has a larger radius.
Both ions feel the same size force.]
D2-15. The loop below is sitting in a uniform magnetic field directed into the page with a size of 750 Gauss.
The field decreases linearly to zero in one-tenth of a second. The radius of the loop is 1.25 cm. Find the
size of the induced voltage across the ends of the loop.
[0.37 mV]
D2-16. The resistance of the loop in the previous problem is 0.3 . Find the size and direction of the induced
current through the loop.
[1.23 mA clockwise]
D2-17. A solenoid has 200 turns. As a bar magnet is pushed into one end of the solenoid at a constant rate, an
induced voltage of 15 mV is developed across the solenoid. Find the rate of the magnetic flux increase
through the solenoid during this time.
[7.5x10-5 T/s]
D2-18. A motor delivers 0.25 horsepower on average at 3000 rpm. It draws 4 Amps of current. Each turn in its
coil has an area of approximately 0.002 m2 and sits in a magnetic field of about 0.04T. About how many
turns does its coil have? How much electrical power does the motor draw if it is plugged into a standard
socket with a 120 V output? What is its power efficiency?
[2914 turns, 480 W, 39%]
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D2-19. A generator delivers an output voltage of the form V (t) = (30 V) sin (20t). Find the maximum and
root mean square voltage differences supplied by the generator. Find the frequency and period of the
output.
[30 V max, 21.2 V rms, 10 Hz, 0.1 s]
D2-20. A coil in a generator is rotated 60 times per second in a magnetic field of 1.5 Teslas. Each turn of the
coil has an area of 10 cm2. The generator puts out a maximum voltage difference of 170 V. How many
turns are there in the coil?
[301]
D2-21. A step-up transformer has a turn ratio of 10:1 and a power efficiency of 95%. Find the ratio of the
output power to the input power, the ratio of the output voltage to the input voltage, and the ratio of the
output current to the input current.
[P2/ P1 = 0.95, V2/ V1 = 10, I2/ I1 = 0.095]
D2-22. A transformer used in lab takes a 120 V input from the wall outlet and delivers a 7 V output to a light
bulb filament. The filament draws 0.04 A of current from the transformer. The efficiency of the
transformer is 90%. Find the current flowing into the transformer from the wall outlet.
[2.6 mA]
D2-23. A 100-Ohm resistor and a 2-milliHenry inductor are connected in series to a 5-V battery. Find the
current through the circuit and the energy stored by the inductor.
[50 mA, 2.5 J]
D2-24. An ac voltage source delivers an rms voltage difference of 40 V to a circuit and an rms current of 80 mA
flows. What is the impedance of the circuit?
[500 ]
D2-25. An ac voltage source delivers an rms voltage of 120 V at a frequency of 60 Hz. Find the amplitude of
the voltage signal.
[170 V]
D2-26. Find the reactances of a 75-Ohm resistor, a 1-microFarad capacitor, and a 5-milliHenry inductor if they
are connected to the voltage source in the previous problem.
[resistor 75, capacitor 2653 , inductor 2 ]